The invention relates to a continuously operating material press for producing, for example, endless composite, particle, fiber rubber and plastic sheets and paper or substances impregnated with synthetic resin. The press typically includes a driven central drum having an outer shell surface and which can be heated or cooled, and reversing drums and a tensioning drum. A circulating endless steel belt is tensioned around and engages a substantial portion of the central drum. The material to be processed into sheet form is guided into the space between the endless belt and the central drum and pressed in the region of the shell surface tightly engaged by the tensioned steel belt.
This type of press is particularly suitable for advantageous production of thin products such as sheets made of paper, textile, fiber, and particle boards. However, the use of these presses for the cross-linkage of sheets made of rubber or thermoplastics has also been known for a long time. In contrast to calender lines, these presses are usually applied in those cases where the short-term exertion of a linear pressure on the material sheet during its passage between two rolls would not be sufficient to expose the material to the desired cross-linking conditions.
Especially when using these presses for the production of particle boards of major thicknesses and/or relatively high material densities, however, the maximum contact pressure, which is limited by the tensile strength of the steel belt proved to be too low. The suggestions which have been made so far for increasing the contact pressure of the steel belt were not suitable for continuously producing particle or fiber boards of a high density. The producers as well as the processing industry have increasingly sought a process for the production of boards which have improved homogeneity and an optimized density profile over the board width in order to obtain products with a higher mechanic stability. However, such a process requires a considerably increased contact pressure acting on the material sheet, compared to apparatuses known in the art.
The German Published Application 41 03 342 discloses a device of this general kind in which the contact pressure exerted by the steel belt on the material is increased by a multitude of rollers with a roller chain. However, the described device presents the disadvantage that once the rollers are worn, the steel belt is damaged and it is not possible to check the rollers when mounted.